1. Field of the invention
The invention relates to methods and substances comprising a biocompatible, non-degradable polymer of stable volume for the purpose of augmenting mammalian tissue.
2. Prior Art
This invention relates to synthetic surgical adhesives/sealants and tissue bulking created by reacting the adhesive tissue augmentation injectable with living in situ tissue. More specifically, a unique tissue cross-linked polyurea-urethane bond formed by reaction of isocyanate capped ethylene oxide diols, triols or polyols with living tissue forms an immobilized, non-biodegradable augmentation of tissue.
Numerous bulking and plastic surgery applications have been published, but none of them teach bulking by means of the novel substance disclosed here and further none of them provide adhesion to tissue. Thus in these prior arts, there is susceptibility to implant migration. The present invention is biocompatible. Prior art bulking substances are also known to be biocompatible, but they are also biodegradable. Biodegradability of an implant in a tissue augmentation procedure is generally not desirable since the benefits conferred by the implanted substance disappear with time.
U.S. Pat. No. 5,785,642 (Wallace et al.) describes a 3-part injectable polymer for treating incontinence. While the patent claims improved resistance to migration, principally when compared with particulate injectables, it does not describe a tissue bond to guard against implant migration. Furthermore, the disclosed invention involves forming a polymer precipitate in situ from a solvent/polymer system. Since the solvent does not entirely become part of the precipitate, then some of the injected solvent volume is eventually lost to absorption into the surrounding tissue. Thus, the invention does not teach a device which has a stable volume once implanted.
U.S. Pat. No. 5,712,252 (Smith) describes a method of augmenting soft tissue in a mammal, which includes injecting keratin into soft tissue. Keratin is a biodegradable substance.
U.S. Pat. No. 5,763,399 (Lee) describes a composition and method for effective revitalization of scar tissue by injecting a bioactive substance having angiogenic activity. The revitalization of scar tissue is intended to augment existing tissue. However, this invention cannot control the extent of augmentation.
U.S. Pat. No. 5,922,025 (Hubbard) describes a permanent, biocompatible material for soft tissue augmentation. The biocompatible material comprises a matrix of smooth, round, finely divided, substantially spherical particles of a biocompatible ceramic material. However, prevention of migration of the ceramic material is not described.
U.S. Pat. No. 5,976,526 (Atala) describes treatment of vesicoureteral reflux, incontinence and other defects using an injectable of bladder cells mixed with a liquid polymeric material. This material is susceptible to biodegradation.
U.S. Pat. No. 5,855,615 (Bley at al) describes a composition for injecting into the urethra comprising a plurality of physiologically acceptable solid polymer particles dispersed in a physiologically acceptable biodissipatable liquid carrier. The solid polymer particles are capable of hydrating to a predetermined volume. The injection volume is therefore not necessarily the same as the final hydrated volume.
U.S. Pat. No. 5,709,854 (Griffith-Cima et al) describes a cell polymeric solution that self-crosslinks, but does not bond to tissue, for the purpose of inducing tissue formation.
One of the primary uses of the present invention is treatment or urinary incontinence. In particular, many women suffer from incontinence caused by childbirth or obesity. The initial treatment for stress incontinence is exercise to strengthen the pelvic floor muscles. If these exercises are ineffective, open surgical repair of the bladder neck is often attempted. Such surgical repair procedures are not successful for all patients. There is also risk associated with open surgical procedures, such as trauma, infection, and risks of anesthesia.
As an alternative to surgical repair, urinary incontinence has been treated by injecting various substances into the tissue surrounding the urethra, i.e., the periurethral tissue, to add bulk to this tissue. The aim of this treatment is to compress the urethra at the level of the bladder neck to impede involuntary flow of urine from the bladder.
Murless has reported the use of sodium morrhuate for the treatment of stress incontinence (J. Obstet. Gynaecol., 45:67-71(1938)). This material was not successful in treating incontinence and pulmonary infarction was an observed complication. Paraffin (Acta Urol. Belg., 23:259-262(1955)) and other sclerosing solutions (Urol. Int., 15:225-244(1963)) have been tried yielding poor results.
Polytetrafluoroethylene particles (TEFLON(trademark), POLYTEF(trademark)) have been used as injectable bulking material with a success rate from 30% to 86% in some studies (J. Urol.,111:180-183(1974); Br. J. Urol.,55:208-210(1983); BMJ 228;192 (1984); J. Urol.,(Paris), 62:39-41(1987); Br. J. Urol., 62:39-41 (1988); Aust. N. Z. J. Surg., 61:663-666 (1966)). The complications associated with this procedure were foreign body granulomas that tended to migrate to distant organs, such as the lungs, liver, spleen and brain (JAMA, 251:3227-3281 (1984)).
Another injectable used recently is glutaraldehyde cross-linked bovine dermal collagen (Med. J. Aust., 158:89-91 (1993); Br. J. Urol., 75:359-363 (1995); Br. J. Urol., 75: 538-542 (1993)). A major problem with the use of collagen was biodegradation with associated decrease in implant volume over time necessitating retreatment (J. Urol., 150:745-747 (1993)). Collagen can also cause adverse immune responses and allergic reactions to bovine collagen have been described (Br. J. Urol., 75:359-363 (1995)).
Other materials have been suggested for use in the treatment of vesicourectal reflux. These substances include polyvinyl alcohol foam (J. Urol., 144:531-533 (1990)), glass particles (J. Urol., 148:645 (1992)), a chondrocyte-alginate suspension (J. Urol., 150:745-747 (1993)) and a detachable silicone balloon (J. Urol., 148:724-728 (1992)), each of these cited journals being incorporated herein by reference.
Injectables have not been suggested for treatment of gastroesophageal reflux disease (GERD), but such use of the disclosed material of this application is envisioned. The material may be injected into the wall of the esophagus to thicken the wall and narrow the gastroesophageal junction into the stomach.
In addition to the need for an immobilized, volume-constant, biocompatible implant, there is also a need to be able to visualize the volume of injected material during and after implantation. It would be preferred to monitor the implant size by non-invasive means. Furthermore, fluoroscopic imaging of the implant would aid in estimation of the implant size and location if follow-up injections are necessary.
In addition, polymerization time of the injected material is an important parameter since the material is typically delivered as a low viscosity solution that may leak from the site after needle removal. The lower the viscosity of the injectable the smaller the needle that may be used.
Finally, there are several pragmatic considerations. For example, the injectable material should not polymerize in the needle of the delivery device so as to necessitate replacement of the needle during the procedure. The solution should be of low viscosity to enable easy delivery of the solution through a 23 G needle.
This invention is directed toward all applications where bulking of tissue provides a functional or aesthetic result. Accordingly, in one of its method aspects, this invention is directed to a method for treating urinary incontinence in a mammal, which method comprises delivery of a single composition comprising a biocompatible prepolymer and a contrast agent to the periurethral tissue of a mammal.
It is an object of the present invention to provide a bulking mass that chemically bonds in situ to living tissue that is biocompatible, elastomeric, and non-biodegradable.
It is another object of this invention to provide an adhesive formulation for tissue augmentation surgery having short bonding and polymerization time.
It is another object of this invention to provide an adhesive bulking material which is non-toxic and non-immunogenic.
It is another object of this invention to provide a low viscosity adhesive bulking material permitting delivery through a 23 G needle.
It is another object of this invention to provide a bulking material that does not undergo appreciable volume change acutely during polymerization or chronically after implantation in tissue.
It is another object of this invention that the bulking material provide fluoroscopic contrast for noninvasive visualization during and after implantation.
It is another object of this invention that the prepolymer composition be gamma sterilizable without appreciable crosslinking of the prepolymer or altering its hydrated tissue bond functionality.
The tissue augmentation of this invention is achieved by reacting the target tissue with a solution of a high molecular weight ethylene oxide polyol, triol or diol end-capped with an organic polyisocyanate.
The tissue augmenting agent of this invention may alternatively be a polyisocyanate capped copolymer of ethylene oxide and polypropylene.
The tissue augmenting agent of this invention may additionally contain, in solution, viscosity lowering inert components such as Perfluronbon or physiologic saline.
It is one primary object of this invention to provide a tissue augmentation solution that is easily applied, cures quickly in situ, and produces a strong tissue bond. The preparations disclosed here can be stored at normal hospital room temperatures, and possess long shelf life.
The invention thus comprises a hydrated, biocompatible tissue-augmentation compound comprised of: living tissue, body derived fluids, at least one NCO-terminated hydrophilic urethane prepolymer derived from an organic polyisocyanate, and oxyethylene-based diols or polyols comprised essentially all of hydroxyl groups capped with polyisocyanate. The prepolymer units may preferably be aliphatic or aromatic isocyanate-capped oxyethylene-based diols or polyols. The molecular weight of the diols or polyols prior to capping with polyisocyanate is prefarably at least 3,000. The polyisocyanate may be a Toluene diisocyanate. The polyisocyanate may be isophorone diisocyanate. The polyisocyanate may be a mixture of Toluene diisocyanate and 6-chloro 2,4,5-trifluoro-1,3 phenylene diisocyanate. The polyisocyanate may be a mixture of Toluene diisocyanate and tetrafluoro-1,3-phenylene diisocyanate. The polyisocyanate may be a mixture of diphenylmethane diisocyanate and 6-chloro 2,4,5-trifluoro-1,3 phenylene diisocyanate. The polyisocyanate may be a mixture of diphenylmethane diisocyanate and tetrafluoro-1,3-phenylene diisocyanate. The polyisocyanate may be para-phenylene diisocyanate. The diols or polyols may be capped with polyisocyanate wherein the isocyanate-to-hydroxyl group ratio is between 1.5 and 2.5. The isocyanate concentration in the prepolymer units may be between 0.05 and 0.8 milliequivalents per gram. The hydrated, biocompatible tissue-augmentation compound may further comprise a biocompatible solvent comprised of acetone to control viscosity and cure time. The hydrated, biocompatible tissue-augmentation compound may further comprise a contrast agent comprised of meglumine. The hydrated, biocompatible tissue-augmentation may further be comprised of a low molecular weight uncapped polyethylene glycol, consisting of PEG 300 as a solvent. The hydrated, biocompatible tissue-augmentation compound may be further comprised of a contrast agent and a biocompatible solvent in combination. The hydrated, biocompatible tissue-augmentation compound may be further comprised of physiological saline. The hydrated, biocompatible tissue-augmentation compound may be comprised of between 10-30% physiologic saline. The hydrated, biocompatible tissue-augmentation compound may be comprised of 10-20% physiologic saline. The hydrated, biocompatible tissue-augmentation compound of may include an injectable material selected from the group comprised of: collagen, silicone, teflon, or pyrolytic carbon coated beads.
The invention also includes a method of preparing a crosslinked hydrophilic, biocompatible hydrated tissue-augmentation compound by reacting together mammalian body tissue, body derived fluids and a prepolymer in a prepolymer-to-water ratio of 3:1 to 20:1, the prepolymer prepared by the steps of: selecting diols or polyols from oxyethylene-based diols or polyols having an average molecular weight of 3,000 to about 30,000, and reacting the diols or polyols with an aliphatic or aromatic polyisocyanate at an isocyanate-to-hydroxyl ratio of about 1.5 to 2.5 so that all of the hydroyl groups of said diols or polyols are capped with polyisocyanate and the resulting prepolymer has an isocyanate concentration of no more than 0.8 milliequivalents per gram. The diols or polyols may be oxyethylene-based diols or polyols. The diols and polyols of step (a) may be dissolved in an organic solvent selected from the group comprising acetonitrile or acetone. The hydrated tissue-augmentation compound may include a solution of non-body derived water, including a saline solution containing 0.9% NaCl. The prepolymer-to-water ratio may be between 3:1 to 20:1. The method may include the step of: washing the bond with a polyfunctional diamine to end isocyanate reactivity.
The invention also includes a prepolymer solution for preparing a hydrophilic, biocompatible tissue augmentation compound characterized by volume conservation, and resistance to decomposition within the body, said prepolymer consisting of: oxyethylene-based diols or polyols having an average molecular weight in excess of 3,000, the diols or polyols having all of the hydroxyl groups capped with an aromatic or aliphatic diisocyanate; and an adhesive tissue augmentation injectable having an isocyanate concentration up to 0.8 meq/gm, an addition liquid such as acetone, uncapped PEG, DMSO, or acetone, and a contrast agent such as meglumine. The prepolymer may include a fluorine containing diisocyanate. The prepolymer may include a polyfunctional amine such as lysine to end isocyanate reactivity, applied after tissue contact. The prepolymer may include the step of: heating the compound to a temperature to between about 65-80 degrees C.; and adding the compound to mammalian body tissue.
The invention also includes a method for treating urinary incontinence in a mammal comprising the steps of: delivering a composition comprising a biocompatible prepolymer, a biocompatible solvent, and a contrast agent to the periurethral tissue of the mammal wherein said prepolymer reacts with all available water at the site of injection and further wherein the delivery results in a polymer matrix of fixed volume formed in situ in the periurethral tissue thereby reducing urinary incontinence in the mammal. The method may include the step of: delivering the composition into the periurethral tissue by an endoscopic process, that is via an endoscope.
The invention also include a method for the delivery of a composition which composition includes a biocompatible prepolymer, a biocompatible solvent, and a water soluble contrast agent to the periurethral tissue of a mammal, which tissue already had deposited therein with an initial amount of the composition which method comprises: visualizing the position of the deposited composition in the periurethral tissue; delivering a prepolymer composition to the periurethral tissue of a mammal containing said deposited composition; reacting the biocompatible polymer with all available water at the delivery site; and delivering additional polymer matrix bonds to the the deposited mass incrementally to controllably increase the resistance of the flow of urine from the bladder. The method may include the step of: visualizing the deposition of compound by selection of one of the processes of the group consisting of: direct visualization, feel, fluoroscopy or ultrasound.
The invention also includes the method for further treating urinary incontinence in a mammal, comprising the step of: implanting a first biocompatible polymer matrix to a periurethral tissue site of a mammal; implanting a second biocompatible polymer matrix to said site at least one day after said first implanted biocompatible polymer matrix has been implanted at said site, wherein said implanted biocompatible polymer matrix is visualized, and a delivery device is directed to the site, and wherein an additional volume of prepolymer solution is delivered incrementally to the site, the prepolymer solution bonding to the periurethral tissue and a previously formed biocompatible polymer mass.
The invention also includes a method for treating GERD in a mammal comprising the steps of: delivering a composition comprising a biocompatible prepolymer, a biocompatible solvent, and a contrast agent to the gastroesophogeal tissue of the mammal wherein the prepolymer reacts with all available water at the site of injection and further wherein the delivery results in a polymer matrix of fixed volume formed in situ in the esophageal tissue thereby reducing GERD in the mammal. The method may include the step of: delivering the composition into the gastroesophageal tissue by an endoscope.
The invention also includes a method for the delivery of a composition which composition includes a biocompatible prepolymer, a biocompatible solvent, and a water soluble contrast agent to the gastroesophageal tissue of a mammal, which tissue already had deposited therein with an initial amount of the deposited composition, which method comprises: visualizing the position of the deposited composition in the esophageal tissue; delivering a prepolymer composition to the esophageal tissue of a mammal containing the deposited composition; reacting the biocompatible polymer with all available water at the delivery site; and delivering additional polymer matrix bonds to the deposited composition incrementally to controllably increase the resistance of the flow of gastric juices from the stomach of the mammal. The method may include the step of: visualizing the deposited composition by selection of one of the processes of the group consisting of: direct visualization, feel, fluoroscopy or ultrasound.
The invention also includes a method for further treating GERD in a mammal, comprising the step of: implanting a first biocompatible polymer matrix to a gastroesophageal tissue site of a mammal; implanting a second biocompatible polymer matrix to the site at least 24 hours (one day) after the first implanted biocompatible polymer matrix has been implanted at the site, wherein the implanted biocompatible polymer matrix is visualized; and directing a delivery device to the site, and incrementally delivering an additional volume of prepolymer solution incrementally to the site, the additional volume of prepolymer solution bonding to esophageal tissue and any previously formed biocompatible polymer mass.
This invention is directed to methods for augmenting tissue, and specifically for treating urinary incontinence and GERD, which methods comprise delivery of a composition comprising a biocompatible tissue-reactive prepolymer, an inert viscosity lowering medium, and a contrast agent to a tissue site.
The tissue-reactive prepolymer types disclosed here differ from inert polymers, in that they bond with tissue to form a bulk inert polymer in situ.
The term xe2x80x9cbiocompatible tissue-reactive prepolymerxe2x80x9d refers to prepolymers which, in the amounts employed, are after curing non-toxic, non-peptidyl, non-migratory, chemically inert, and substantially non-immunogenic when used internally in a mammal and which are substantially insoluble in the periurethral tissue. The bonded biocompatible polymer does not substantially change volume over time and does not migrate to distant organs within the body.
A uniquely flexible, biocompatible, non-biologic tissue bond can be produced by cross-linking hydrated polymer gels to nitrogenous components found in living tissue. The hydrated tissue augmentation is formed by reacting polymeric monomer units with tissue, at least 75% of which are oxyethylene-based diols or polyols with molecular weight exceeding 10,000. The prepolymer is preferably comprised of hydroxyl groups of diols or polyols substantially all capped by polyisocyanate, where non-polymerized polyisocyanate accounts for less than 4% (v/v) of the adhesive tissue augmentation injectable. Amines in the tissue serve to polymerize tissue with the adhesive tissue augmentation injectable. Water mixed or acquired at the bond site generates additional amine through reaction with polyisocyanate and serves to polymerize the bulk of the bond.
The addition of an organic liquid lacking an accessible OH, and preferably one formed in the Krebs cycle can be used to adjust cure time and prepolymer viscosity. The organic liquid must be completely miscible with the prepolymer, and essentially polar. When the addition liquid is miscible it also becomes trapped permanently within the hydrated polymer matrix formed when injected into tissue. Trapping the addition liquid is essential to preserving hydrated polymer matrix volume. Liquids not occurring naturally within the body may also be used, such as glycerol, but these liquids may not share the same biocompatibility.
The addition of aqueous solution to the prepolymer just before application represent and embodiment of the present invention, and in the case of aliphatic prepolymer compositions, typically provide long ( greater than 10 minutes) pot life. Where xe2x80x9cpot lifexe2x80x9d is defined as that period of time just after introduction of the aqueous component to the polyol and just before gelation sufficient to prevent ejection through the treatment needle.
Any of the previously known tissue bulking compositions can be combined with the present invention. Some of these must be added just prior to injection, such as any of several animal components, be they autologous or zenologous. In particular, collagen may be used. All of the inert additives may be added during device packaging, and form the original ingredients of the composition. For example, teflon particles and fibers, pyrolytic carbon coated beads, silicone beads, etc may be added to the composition. Also, tissue initiators may be added. For example, beta-glucan may be added to promote fibrosis. However, all of the above additions are likely to promote tissue reaction, and therefore must be considered less biocompatible.
The diols and polyols used in the tissue bond predominately or exclusively are polyoxyalkylene diols or polyols whose primary building blocks are ethylene oxide monomer units. Preferably, 75% of the units should be ethylene oxide. Other adhesive tissue augmentation injectable systems may contain proportions of propylene oxide or butylene oxide units in the polyols. The use of these constituents is specifically avoided in the present invention.
To obtain desirable tissue augmentation injectable viscosity and bond strength high molecular weight ethylene oxide-based diol and polyols are used to prepare the tissue augmentation injectable. The diol or polyol molecular weight prior to capping with polyisocyanate should be at least 8000 MW, preferably greater than 10,000 MW. Triols (trihydroxy compounds) in the preparation of the polyols are the precursors to preparation of the prepolymer of this invention. There are many suitable triols: triethanolamine, trimethylolpropane, trimethylolethane, and glycerol.
Alternatively, tetrols may be used. Triol- or tetrol-based polyols are capped with polyfunctional isocyanate, preferably a diisocyanate.
Alternatively, diols may be used. High molecular weight polyethylene glycols are satisfactory. Diols are to be end capped with diisocyanates in addition with crosslinking compounds. Polyfunctional amines and isocyanates are suitable as crosslinking agents. Mixtures of diols and polyols are also suitable.
The prepolymer of this invention is formed by reacting the hydroxyl groups of the diols or polyols with polyisocyanates. The choice of the polyisocyanate will depend on factors well known in the art, including precursor choice, cure time, and mechanical properties of the tissue bond formed by reacting the prepolymer with tissue.
The choice of precursor is not independent of the choice of polyisocyanate. The choice must afford sufficient crosslinking to the tissue so as not to compete detrimentally with internal crosslinking initiated with the addition of water to the bond. This competition can be favorably biased in favor of the tissue bonding reaction by heating the tissue augmentation injectable, reducing its viscosity by addition of solvents, or adding macroscopic hygroscopic fillers. The choice may also afford rapid bulk polymerizationxe2x80x94typically less than 60 seconds. However, in the case of urethral or esophageal bulking a longer pot time is desired, typically about 15-30 minutes. Increase in bulk polymerization time can be accomplished by adding acetone or selecting a less reactive polyisocyante.
Aliphatic or cycloaliphatic polyisocyanates are preferred in the above embodiments because they result in more biocompatible prepolymers.
Examples of suitable (listed in descending order of suitability) polyfunctional isocyanates are found in the literature, and include the following and commonly obtained mixtures of the following:
9,10-anthracene diisocyanate
1,4-anthracenediisocyanate
benzidine diisocyanate
4,4xe2x80x2-biphenylene diisocyanate
4-bromo-1,3-phenylene diisocyanate
4-chloro-1,3-phenylene diisocyanate
cumene-2,4-diisocyanate
Cyclohexylene-1,2-diisocyanate
Cyclohexylene-1,4-diisocyanate
1,4-cyclohexylene diisocyanate
1,10-decamethylene diisocyanate
3,3xe2x80x2dichloro-4,4xe2x80x2-biphenylene diisocyanate
4,4xe2x80x2diisocyanatodibenzyl
2,4-diisocyanatostilbene
2,6-diisocyanatobenzfuran
2,4-dimethyl-1,3-phenylene diisocyanate
5,6-dimethyl-1,3-phenylene diisocyanate
4,6-dimethyl-1,3-phenylene diisocyanate
3,3xe2x80x2-dimethyl-4,4xe2x80x2diisocyanatodiphenylmethane
2,6-dimethyl-4,4xe2x80x2-diisocyanatodiphenyl
3,3xe2x80x2-dimethoxy-4,4xe2x80x2-diisocyanatodiphenyl
2,4-diisocyantodiphenylether
4,4xe2x80x2-diisocyantodiphenylether
3,3xe2x80x2-diphenyl-4,4xe2x80x2-biphenylene diisocyanate
4,4xe2x80x2-diphenylmethane diisocyanate
4-ethoxy-1,3-phenylene diisocyanate
Ethylene diisocyanate
Ethylidene diisocyanate
2,5-fluorenediisocyanate
1,6-hexamethylene diisocyanate
Isophorone diisocyanate
4-methoxy-1,3-phenylene diisocyanate
methylene dicyclohexyl diisocyanate
m-phenylene diisocyanate
1,5-naphthalene diisocyanate
1,8-naphthalene diisocyanate
polymeric 4,4xe2x80x2-diphenylmethane diisocyanate
p-phenylene diisocyanate
p,pxe2x80x2,pxe2x80x3-triphenylmethane triisocyanate
Propylene-1,2-diisocyanate
p-tetramethyl xylene diisocyanate
1,4-tetramethylene diisocyanate
2,4,6-toluene triisocyanate
trifunctional trimer (isocyanurate) of isophorone diisocyanate
trifunctional biuret of hexamethylene diisocyanate
trifunctional trimer (isocyanurate) of hexamethylene diisocyanate
Bulk curing of the tissue bond of this invention is achieved by using stoichiometric amounts of reactants. The isocyanate-to-hydroxyl group ratio should be as low as possible without inhibiting bonding function, typically 2+/xe2x88x9210%. Higher ratios achieve adequate bonds but result in excessive amounts of monomer in the bond. The time period used to cap the polyol or diol is dependent on the polyisocyanate used. Methods for polyisocyanate capping of polyols are well known.
In forming the tissue augmentation, organic solvents are usefully present during the polymerization with tissue to enable a greater tolerance of excessive isocyanate that may disrupt hydrated polymer formation. Varying the amount of solvent also varies the viscosity of the tissue augmentation injectable. The porosity of the tissue bond can be decreased by reducing the viscosity of the prepolymer, and conversely. Useful solvents are ethanol, acetonitrile, saline and acetone.
A prepolymer-aqueous solution may be premixed in ratios up to 1:1 to initiate polymerization and curing. Alternative, the prepolymer may be delivered to the site and then followed with an injection of difunctional amine to initiate bulk polymerization. Such methods are useful in obtaining near instantaneous tackiness and fixation.
The prepolymer-to-aqueous solution ratio should be 1:1 to about 20:1, preferably about 5:1 to about 10:1. The ratio is often chosen such that the in situ cured mass approximates the surround tissue modulus. Bulk polymerization time, bond strength and bond porosity increases in the preferred ratios when the prepolymer content increases.
The implantability of the cured prepolymer of this invention relates to the bond""s ability to present a surface of water to adjacent tissue. When the prepolymers of this invention are used in contact with water-containing tissues, the ethylene oxide segments of the bond attract and complex with water molecules. Consequently, the surface presented to living cells is predominately a layer of water. The protective layer of water renders the underlying synthetic polymeric tissue bond noninteractive with proteins. Consequently, the cured prepolymer does not remove or denature proteins from the environment in which it is implanted.
The prepolymer may also be mixed with a contrast agent or radiopaque material. The contrast agent may become part of the polymer matrix as are the water miscible types, or suspended in the polymer matrix as in the water insoluble type. Water soluble contrast agents include metrizamide, iopamidol, iothalamate sodium, iodomide sodium, and meglumine. Examples of water insoluble contrast agents include tantalum, tantalum oxide, gold, tungsten, platinum, and barium sulfate.
The examples that follow are given for illustrative purposes and are not meant to limit the invention described herein.